568 Proceedings of the Royal Irish Academy. 



and in tlie case of the foraminiferons structure shown in the drawing 

 it might be a portion of a radiolarian (see PI. XI., fig. 2). As, how- 

 ever, the characters shown by the thin section under polarized light 

 did not satisfactorily show what might be the nature of the brown 

 granular matrix, a section was prepared and submitted to the action 

 of dilute hydrochloric acid. The carbonates of iron and lime were 

 thus removed, and there remained unacted upon a brown, largely re- 

 ticulated, residual part, which under crossed nicols behaved as an 

 isotropical body, while here and there chips or small flakes of double 

 refracting colourless minerals showed themselves, some with the weak 

 refrangibility of the microlites characteristic of most natural glasses, 

 and some large and more markedly refracting presented the characters 

 of a sanadine or nepheline. This brown residue appeared to be quite 

 black by transmitted light, but by ordinary difEused light showed a 

 brown colour and a granular stnicture, presenting the appearance, 

 as a whole, of a dark brown soft sugar. From this test the inference 

 is drawn that the brown matter in question is mainly composed of 

 particles of pumice enclosing fragments of spicules, radiolarians, and 

 other such marine forms. 



Considering the frequence of the volcanic outbursts during 

 the Carboniferous period, and the proved existence already referred 

 to of eruptive rocks in the formation, it would be quite in con- 

 formity therewith to find proofs of the ejection of pumice as a 

 part of tlie volcanic activity of the period. And presuming that 

 the shale beds represent deep-sea deposits formed relatively far from 

 land, it might be expected that they would show the presence of 

 pumice when carefully examined. This association of pumice with 

 deep-sea deposits is one of the facts markedly brought out by the 

 soundings of the " Challenger'' expedition. As to the presence of 

 the fossil remains with the pumice that is easily accounted for, if con- 

 sideration be taken of the fact that pumice not only floats at the 

 surface of water, but that as a result of a volcanic eruption immense 

 extents of ocean surface may be covered with a thick bed of it. One 

 of the many notable instances of this came under my notice imme- 

 diately after the eruption of Krakatoa. A gentleman residing in 

 Dublin, and connected with a large firm of importers in the city, 

 received from a captain of a ship which arrived from Eastern waters, 

 and which had been in the neighbourhood of the celebrated eruption, 

 specimens of the mass of pumice with which the surface of the sea had 

 been covered in consequence of that eruption, and I was able to get 

 from him the following details relative thereto, giving also the ex- 



